Drug Groups

approved; investigational

Description

Leflunomide is a pyrimidine synthesis inhibitor belonging to the DMARD (disease-modifying antirheumatic drug) class of drugs, which are chemically and pharmacologically very heterogeneous. Leflunomide was approved by FDA and in many other countries (e.g., Canada, Europe) in 1999.

Indication

For the management of the signs and symptoms of active rheumatoid arthritis (RA) to improve physical function and to slow the progression of structural damage associated with the disease. Has also been used for the prevention of acute and chronic rejection in recipients of solid organ trasnplants and is designated by the FDA as an orphan drug for this use.

Pharmacology

Leflunomide is a pyrimidine synthesis inhibitor indicated in adults for the treatment of active rheumatoid arthritis (RA). RA is an auto-immune disease characterized by high T-cell activity. T cells have two pathways to synthesize pyrimidines: the salvage pathways and the de novo synthesis. At rest, T lymphocytes meet their metabolic requirements by the salvage pathway. Activated lymphocytes need to expand their pyrimidine pool 7- to 8-fold, while the purine pool is expanded only 2- to 3-fold. To meet the need for more pyrimidines, activated T cells use the de novo pathway for pyrimidine synthesis. Therefore, activated T cells, which are dependent on de novo pyrimidine synthesis, will be more affected by leflunomide's inhibition of dihydroorotate dehydrogenase than other cell types that use the salvage pathway of pyrimidine synthesis.

Toxicity

LD₅₀=100-250 mg/kg (acute oral toxicity)

Affected Organisms

Biotransformation

Primarily hepatic. Leflunomide is converted to its active form following oral intake.

Absorption

Well absorbed, peak plasma concentrations appear 6-12 hours after dosing

Half Life

2 weeks

Protein Binding

>99.3%

Elimination

The active metabolite is eliminated by further metabolism and subsequent renal excretion as well as by direct biliary excretion. In a 28 day study of drug elimination (n=3) using a single dose of radiolabeled compound, approximately 43% of the total radioactivity was eliminated in the urine and 48% was eliminated in the feces. It is not known whether leflunomide is excreted in human milk.
Many drugs are excreted in human milk, and there is a potential for serious adverse reactions in nursing infants from leflunomide.

Distribution

* 0.13 L/kg

References

External Links